1. Field of the Invention
The present invention relates to an angular velocity sensor for use in technologies, such as navigation systems for automobiles, compensation systems for camera shaking, and robot attitude controlling apparatuses.
2. Description of the Related Art
An angular velocity sensor is generally known which comprises a supporting substrate, a pair of support-fixing portions disposed in the supporting substrate, a first supporting beam connected to the support-fixing portion, a first oscillator supported with the first supporting beam, a second supporting beam connected to the first oscillator, a second oscillator supported with the second supporting beam oscillating in the direction that a Coriolis force is generated, driving means for driving these oscillators in a predetermined direction, and detecting means for detecting the displacement of the second oscillator due to the Coriolis force applied to the second oscillator.
Referring to FIGS. 9 and 10, a conventional angular velocity sensor 40 will now be described.
Numeral 31 represents a supporting substrate formed of Pyrex glass and a recess portion 31a is disposed in the central portion thereof.
Numeral 32 denotes a frame-shaped supporting body joined to a peripheral portion of the supporting substrate 31 by anodic bonding and the frame-shaped supporting body 32 is formed of silicon in a rectangular shape. In the frame-shaped supporting body 32, from four portions inside the crosspieces thereof disposed separated in the Y-axis direction from each other, first supporting beams 33a, 33b, 33c, and 33d (referred to generically below as first supporting beams 33) extend respectively in the y-axis direction. In the frame-shaped supporting body 32, the four portions fixed to the first supporting beams 33 are designated as support-fixing portions 32a. 
End portions of the first supporting beams 33 are joined to outsides of the crosspieces of an oscillator 34, which is disposed in the inner periphery of the frame-shaped supporting body 32. The first supporting beams 33 support the oscillator 34 and allow it to oscillate in the x-axis direction. The oscillator 34 is roughly rectangularly frame-shaped and outsides of crosspieces thereof disposed separated in the y-axis direction from each other are joined to four portions of the first supporting beams 33. In the oscillator 34, from the four portions inside the crosspieces thereof disposed separated in the X-axis direction from each other, second supporting beams 35a, 35b, 35c, and 35d (referred to generically below as second supporting beams 35) extend respectively in the x-direction, and end portions thereof are respectively joined to the outside surfaces of a second oscillator, a load oscillator 36, which will be described later. In addition, the first supporting beams 33 and the second supporting beams 35 have an orthogonal relationship and the first supporting beams 33 extend in the Y-axis direction while the second supporting beams 35 extend in the X-axis direction.
The load oscillator 36, which is formed in a roughly rectangular plane, is disposed in the inner periphery of the oscillator 34 and is supported by the second supporting beams 35 which allow it to oscillate in the Y-axis direction.
Numerals 37, 37 represent driving portions serving as driving means disposed in the oscillator 34 and the frame shaped supporting body 32, and separated in the X-direction from each other. The driving portions 37, 37 are formed of driving electrodes 37a and 37b respectively disposed in outer surfaces of crosspieces of the oscillator 34 separated in the X-axis direction and driving electrodes 37c and 37d respectively disposed in inner surfaces of the frame-shaped supporting body 32, opposing the driving electrodes 37a and 37b. 
Numerals 38, 38 represent detecting portions serving as detecting means disposed in the oscillator 34 and the load oscillator 36, separated in the Y-direction from each other. The detecting portions 38, 38 are formed of detecting electrodes 38a and 38b respectively disposed in inner surfaces of crosspieces of the oscillator 34 separated in the Y-axis direction and detecting electrodes 38c and 38d respectively disposed in outer surfaces of the load oscillator 36, opposing the detecting electrodes 38a and 38b. 
In addition, the oscillator 34, the load oscillator 36, the first supporting beams 33, and the second supporting beams 35 are integrally formed by working the same silicon base plate as the frame-shaped supporting body 32.
The conventional angular velocity sensor 40 is formed as described above and the operation thereof will now be described.
The load oscillator 36 and the oscillator 34 oscillate in the X-axis direction by electrostatic forces generated by applying respective ac voltages, which are 180xc2x0 out of phase with each other and on which respective dc voltages are superimposed, to the driving electrodes 37a and 37c and the driving electrodes 37b and 37d. At this time, the oscillating of the load oscillator 36 in the X-axis direction is possible by the deflection of the first supporting beams 33.
During the oscillation of the load oscillator 36 in such manner, when the angular velocity sensor 40 is rotated by application of an angular velocity xe2x80x9cxcexa9xe2x80x9d about the Z-axis passing through the center of the load oscillator 36, a Coriolis force is generated in the Y-axis direction. Therefore, the load oscillator 36 oscillates also in the Y-axis direction. At this time, the oscillating of the load oscillator 36 in the Y-axis direction is possible by deflection of the second supporting beams 35.
When the load oscillator 36 oscillates in the Y-axis direction, the electrostatic capacity between the detecting electrodes 38a and 38c and the electrostatic capacity between the detecting electrodes 38b and 38d increase and decrease. Accordingly, these varying electrostatic capacities are converted to voltages and differentially amplified, so that a value of the rotational angular velocity xe2x80x9cxcexa9xe2x80x9d can be obtained.
However, since in the conventional angular velocity sensor 40, the supporting substrate 31 formed of Pyrex glass and the frame-shaped supporting body 32 formed of silicon are of a single-piece structure bonded together by anodic bonding, when the ambient temperature is changed, a tensile stress or a compressive stress is generated in the bonded portion due to the difference between respective thermal expansion coefficients.
When the thermal expansion coefficient of the supporting substrate 31 is larger than that of the frame-shaped supporting body 32, for example, strain is generated so that respective joining portions of the frame-shaped supporting body 32 to the first supporting beams 33 for driving are spread in the outside directions as shown by the arrows xe2x80x9ccxe2x80x9d. This strain causes tensile forces to be applied in the outside directions in the first supporting beams 33 so as to increase the resonance frequency of driving. In this case, since the resonance frequency of detecting is not changed, the difference between the resonance frequencies of driving and detecting is increased, resulting in reduced detecting sensitivity.
This problem has a large effect especially on an angular velocity sensor designed to be highly sensitive by reducing the difference between the resonance frequencies of driving and detecting. Therefore, the conventional angular velocity sensor 40 has to be designed to increase the difference between the resonance frequencies of driving and detecting in advance for preventing reduction in detecting sensitivity due to the increased difference between the resonance frequencies of driving and detecting. Consequently, it has become a problem that angular velocity sensors having high sensitivity cannot be manufactured.
Accordingly, it is an object of the present invention to provide an angular velocity sensor having increased detecting sensitivity by reducing the difference between the resonance frequencies of driving and detecting due to the effect of different thermal expansion coefficients of the supporting substrate and the sensor element substrate.
An angular velocity sensor according to an embodiment of the present invention comprises: a supporting substrate; a support-fixing portion disposed in the supporting substrate; a first supporting beam connected to the support-fixing portion; a first oscillator supported with the first supporting beam; a second supporting beam connected to the first oscillator; a second oscillator supported with the second supporting beam oscillating in the direction that a Coriolis force is generated; driving means or elements for driving the first oscillator and the second oscillator in a predetermined direction; and detecting means or elements for detecting the displacement of the second oscillator caused by the Coriolis force applied to the second oscillator, wherein the first supporting beam extends at least in the direction orthogonal to the oscillating direction of the first oscillator, both ends of the first supporting beam being connected to the first oscillator, and a longitudinally intermediate portion of the first supporting beam being joined to the support-fixing portion.
According to one aspect of the invention, a sensor element comprising a support-fixing portion and movable portions such as a first oscillator is formed of a different material from that of a supporting substrate. For example, the supporting substrate is formed of Pyrex glass while the sensor element is formed of a silicon base plate. The movable portions are supported by, for example, a pair of spaced support-fixing portions via first supporting beams. Since the pair of support-fixing portions are fixed to the supporting substrate at an interval by, for example, anodic bonding, etc., when temperature is changed, the supporting substrate expands and contracts due to thermal expansion of the material while the sensor element also expands and contracts. However, when the coefficient of thermal expansion differs from the supporting substrate to the sensor element, the sensor element is subjected to the strain by the difference between coefficients of thermal expansion. Since the sensor element is fixed to the supporting substrate via the pair of support-fixing portions, the pair of support-fixing portions are directly subjected to the elastic strain (displacement) due to the difference between coefficients of thermal expansion.
When the center of the strain is in the center of the sensor element (supporting substrate), the strain expands or contracts radially and concentrically from the center thereof. Therefore, this expanding or contracting strain increases in proportion to the spacing between the pair of support-fixing portions.
The lines of action of the strain range within the width of the joining portions of the pair of support-fixing portions to the first supporting beams. When the width of the joining portions of the pair of support-fixing portions is large, a component of the strain is also generated in the longitudinal (extending) direction of the first supporting beams. When the joining portions are formed in a small width so that the acting range of the strain is reduced, i.e., lines of action of the strain converge at the line connecting the centers of the pair of support-fixing portions, the component of the strain in the longitudinal direction of the first supporting beams can be reduced.
When such the strain is acting in the direction of the line connecting the centers of the pair of support-fixing portions, i.e., the same as the driving direction, both sides of the longitudinally intermediate portion of the first supporting beam are equally deflected due to the strain because both sides of the support-fixing portion of the first supporting beam are symmetrical, so that the pair of first supporting beams are deformed or deflected in a xe2x80x9c less than xe2x80x9d shape or an inverted xe2x80x9c less than xe2x80x9d shape. Thereby the strain is absorbed by the deformation or the deflection so as not to affect the movable parts such as the first oscillator. Therefore, the stress due to the strain is scarcely generated in the extending direction of the first supporting beams.
Since the stress acting in the extending direction is a principal reason for variations in the resonance frequency in the driving direction, in this structure, the driving frequency is not affected by the thermal strain. Likewise, the resonance frequency of the second supporting beam in the detecting direction is not changed by the thermal strain because the second supporting beam is not directly joined to the substrate. Consequently, the difference between resonance frequencies in driving and detecting directions is not changed by variations in temperatures thereby preventing variations in detecting sensitivity. Accordingly, it is possible to provide an angular velocity sensor having a high sensitivity by making the mechanical resonance frequencies for driving and detection close to each other.
In addition, shapes of the pair of support-fixing portions and the first supporting beams are formed as described above, so that the strain due to the dispersion during manufacturing in addition to the strain due to variations in temperatures is absorbed by deformation or deflection of the first supporting beams so as to maintain the difference between mechanical resonance frequencies in driving and detecting to be constant. As a result, variations in detecting sensitivity is prevented, thereby stabilizing the operation characteristics.
According to another embodiment of the invention, the support-fixing portions are disposed in two positions outside the first oscillator separated from each other in the oscillating direction of the first oscillator, a width of a joining portion of each of the support-fixing portions to the first supporting beam being formed to be less than that of a root portion of the support-fixing portion.
According to this embodiment, the joining portion of each of two support-fixing portions supporting longitudinally intermediate portion of the first supporting beam is formed to be small in width. That is, the joining portion extending from the root portion of the support-fixing portion is formed to be tapered or the joining portion is formed in a short beam-shape, so that the thermal stress applied to the first supporting beams from the pair of support-fixing portions is directed to a straight line orthogonal to the longitudinal direction of the first supporting beam, thereby enabling focusing of the effect by the thermal stress from the pair of support-fixing portions on a straight line to reduce it all the more. As a result, it is possible to suppress the fluctuation of output sensitivity over an wide temperature range.
When the end portion of the support-fixing portion connected to the first supporting beam is large in width, for example, the strain due to the stress is applied on the overall surface of the support-fixing portion, so that at two joining positions between this support-fixing portion and the first supporting beam strain is generated due to the tensile stress or the compressive stress toward the outside or inside of the first supporting beam. In contrast, when the end portion of the support-fixing portion is small in width, the strain due to the stress is focused on a straight line connecting end portions of the opposing pair of the support-fixing portions thereby being absorbed by uniform deflection of the pair of the first supporting beams.
According to still another embodiment, the first oscillator is formed of a rectangular frame body, the second oscillator being rectangular and oscillating within the first oscillator, and wherein the second supporting beam extends in the same direction as the oscillating direction of the first oscillator, both ends of the second supporting beam being connected to the second oscillator, and a longitudinally intermediate portion of the second supporting beam being joined to the first oscillator.
According to this embodiment, both ends of the first supporting beam are connected to the first oscillator formed in a frame-body shape. The strain generated in the pair of support-fixing portions is absorbed with the first supporting beams so as not to affect the oscillation of the second oscillator. Therefore, the second oscillator oscillates efficiently in the same direction as that of the first oscillator without the effect of the strain while oscillates in the direction that a Coriolis force is generated. That is, the driving direction of oscillators and the detecting direction of a Coriolis force are geometrically well-balanced. This further improve the detection sensitivity.
According to still another embodiment, the first supporting beam is formed of plural arm portions extending in the direction orthogonal to the oscillating direction of the first oscillator and folded portions for connecting each arm portion together in a folded state extending in the same direction as the oscillating direction of the first oscillator.
According to such a configuration, when the first oscillator oscillates owing to the driving means, plural arm portions connected together in a folded state expand and contract. Therefore, the first oscillator oscillates easily in the oscillating direction enabling the amplitude to be increased. In addition, the resonance frequency of the first oscillator can be maintained to be stable regardless of the amplitude of the first oscillator, enabling the first oscillator to oscillate at the large amplitude so as to improve the detecting sensitivity of angular velocity.
According to an aspect of this embodiment, lengths of the folded portions are less than those of the arm portions.
Thereby, the first oscillator moves easily in the oscillating direction while can be formed to be difficult to oscillate in the direction orthogonal to the oscillating direction. Consequently, the first oscillator can oscillate only in the oscillating direction restricting the oscillation in the direction orthogonal to the oscillating direction.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.